The present invention relates to concrete stave building structures, and in particular silos, wherein both economy and flexibility is achieved by utilizing the high compressive strength of concrete and the tensile strength of encircling steel hoops. The steel hoops encircle the concrete staves of the silo and after pretensioning function to hold the polygon formed by the stave elements in compression. To accomplish the foregoing encirclement of the concrete stave elements, there is disclosed herein an improved mechanism for gripping the hoops which consists of a plurality of adjoining angles each of which is provided with a substantially semi-circular channel such that when the angles are positioned in abutting relationship, a substantially circular passageway is defined, and an adjustable bolting mechanism permitting the semicircular channels to grip the hoop after pretensioning so as to hold the stave segments of the silo in compression.